Obstructive sleep apnea (OSA) is a medical condition that is caused by a blockage of the airway, which usually occurs when the soft tissue in the throat collapses and closes during sleep. According to the National Institutes of Health, OSA affects more than twelve million Americans. During each apnea event, the brain briefly arouses the sufferer in order to initiate the resumption of breathing. This type of sleep, however, is extremely fragmented and of poor quality. When left untreated, OSA may result in high blood pressure, cardiovascular disease, weight gain, impotency, headaches, memory problems, job impairment, and motor vehicle crashes. Despite the seriousness of OSA, a general lack of awareness among the public and healthcare professionals results in the vast majority of OSA sufferers remaining undiagnosed and untreated.
In the human body, the air filled space between the nasal cavity and the larynx is referred to as the upper airway. The most critical part of the upper airway associated with sleep disorders is the pharynx. The pharynx has three different anatomical levels. The nasopharynx is the upper portion of the pharynx located in the back of the nasal cavity. The oropharynx is the intermediate portion of the pharynx containing the soft palate, the epiglottis, and the curve at the back of the tongue. The hypopharynx is the lower portion of the pharynx located below the soft tissue of the oropharynx. The oropharynx is the section of the pharynx that is most likely to collapse due to the high prevalence of soft tissue structure, which leaves less space for airflow. The hypopharynx lies below the aperture of the larynx and behind the larynx, and extends to the esophagus.
As is well known to those skilled in the art, the soft palate and the tongue are both flexible structures. The soft palate provides a barrier between the nasal cavity and the mouth. In many instances, the soft palate is longer than necessary and it extends a significant distance between the back of the tongue and the posterior pharyngeal wall.
Although the muscles relax throughout the body during sleep, most of the muscles of the respiratory system remain active. During inhalation, the diaphragm contracts and causes negative pressure to draw air into the nasal cavity and mouth. The air then flows past the pharynx, through the trachea and into the lungs. The negative pressure causes the tissue of the upper airway to deform slightly, which narrows the airway passage. In apneic patients, the soft palate, the tongue, and/or the epiglottis collapse against the posterior pharyngeal wall to block airflow into the trachea. As the airway narrows, airflow through the pharynx becomes turbulent which causes the soft palate to vibrate, generating a sound commonly known as snoring.
During sleep, humans typically experience brief obstructions of airflow and/or small decreases in the amount of airflow into the trachea and lungs. An obstruction of airflow for more than ten seconds is referred to as apnea. A decrease in airflow by more than fifty percent is referred to as hypopnea. The severity of sleep disorders is measured by the number of apneas and hypopneas that occur during every hour of sleep. If apnea or hypopnea occurs more than five times per hour, most medical personnel diagnose the individual as having an upper airway resistance problem. Many of these patients exhibit symptoms related to sleep disorders including sleepiness during the day, depression, and difficulty concentrating.
Individuals having ten or more episodes of apnea or hypopnea during every hour of sleep are officially classified as having obstructive sleep apnea syndrome. As the airway is obstructed, the individual makes repeated attempts to force inhalation. Many of these episodes are silent and are characterized by movements of the abdomen and chest wall as the individual strains to draw air into the lungs. Typically, episodes of apnea may last a minute or more. During this time, oxygen levels in the blood will decrease. Ultimately, the obstruction may be overcome by the individual generating a loud snore or awakening with a choking feeling.
When an individual is awake, the back of the tongue and the soft palate maintain their shape and tone due to their respective internal muscles. As a result, the airway through the pharynx remains open and unobstructed. During sleep, however, the muscle tone decreases and the posterior surface of the tongue and the soft palate become more flexible and distensible. Without normal muscle tone to keep their shape and to keep them in place either alone or as a group, the posterior surface of the tongue, the epiglottis, and the soft palate SP tend to easily collapse to block the airway.
One known treatment, commonly referred to as continuous positive airway pressure (CPAP), is currently the “gold standard” for treating OSA and operates by delivering air into a patient's airway through a specially designed nasal mask or pillow. The flow of air creates positive pressure when the patient inhales to keep the airway open. Although CPAP is considered by many to be an effective non-surgical treatment for the alleviation of snoring and obstructive sleep apnea, patients complain about discomfort caused by the mask and hoses, including bloating, nasal drying, and dry eyes. As a result, patient compliance for CPAP is only about 40%.
Surgical treatments have also been used to treat OSA. One such treatment is referred to as uvulopalatopharyngoplasty, which involves removing about 2 cm of the trailing edge of the soft palate to reduce the soft palate's ability to flutter between the tongue and the pharyngeal wall. Another procedure uses a surgical laser to create scar tissue on the surface of the soft palate, which reduces the flexibility of the soft palate for reducing snoring and/or closing of the air passage. Yet another procedure, commonly referred to as cautery-assisted palatal stiffening operation (CAPSO), is an office-based procedure performed under local anesthesia whereby a midline strip of soft palate mucosa is removed, and the wound is allowed to heal whereupon the flaccid palate is stiffened.
Surgical procedures such as those mentioned above continue to have problems. More specifically, the area of tissue that is surgically treated (i.e., removal of palatal tissue or scarring of palatal tissue) is often larger than is necessary to treat the patient's condition. In addition, the above-mentioned surgical procedures are often painful with extended, uncomfortable healing periods. For example, scar tissue on the soft palate may present a continuing irritant to the patient. Furthermore, the above procedures are not reversible in the event of adverse side effects.
Surgical implants have also been used to treat OSA. One such implant system, sold under the name AIRvance by Medtronic, Inc. of Minneapolis, Minn., uses a titanium screw that is inserted into the posterior aspect of the mandible at the floor of the mouth. A loop of suture is passed through the tongue base and attached to the mandibular bone screw. The procedure achieves a suspension or hammock of the tongue base making it less likely for the base of the tongue to prolapse during sleep. The use of the screw style bone anchor increases the risk of damage to the teeth or the nerve roots and or vasculature for the teeth.
Another known tongue suspension device similarly utilizes a bone screw in the mandible, but has the advantage of being adjustable. The device utilizes a flexible shape memory anchor within the tongue that is shaped similar to a grappling hook to engage the tissue within the tongue base. It is placed through a small incision in the sub-mental region and the suture is attached to a spool-like component attached to the mandible. Two to four weeks after healing, a small incision is made under the chin and a screw is turned to tighten the suture, thus pulling the device forward. While the device provides a simplified installation technique from within the sterile space, the anchors suffered from a high rate of device fracture and failure due to loading within the tongue musculature. Additionally, the risk of damage to the teeth or the nerve roots for the teeth is similar in both devices.
U.S. Pat. No. 7,367,340 describes the use of an element that is anchored to the mandible and is capable of applying force within the tongue to prevent the tongue from collapsing during sleep. In the embodiments described, the device consists of an element that is attached to the mandible though drilling of the mandible to provide a rigid point of fixation. The method of attachment produces essentially the same risk to the dental anatomy and nerve structures within the mandible.
This risk of damage by the above-described devices is illustrated by FIG. 1, which shows the typical mandible placement of a bone screw with a suspension fiber. As the screw extends into the mandible as shown, it may potentially strike the nerves, vasculature or teeth depending upon placement.
In order to avoid the risk of damage to the bone or nerves, an alternative approach that utilizes a flexible soft tissue anchor is illustrated in FIG. 2. In this embodiment, the anchor for the suspension loop is placed within the soft tissue of the sub-mental region and the suspension element is fixed to the soft flexible anchor. While this method avoids the issues associated with the placement of a bone anchor or screw in the mandible, it results in a more vertical angle θ2 of fixation for the suspension loop. When comparing the foregoing illustrations, it can be seen that the angle θ2 is larger for the soft tissue anchor system than the angle θ1 for the bone anchor device. It is possible that the anchor, if placed to far posterior to the infra-mandibular margin, may result in a vertical compression of the tongue base instead of anterior displacement of the tongue. Therefore, it is desirable to provide an anchor system that more closely approximates the resultant angle of suspension.
Given the disadvantages described above, there remains a need for a tongue suspension device that provides a point of fixation relative to the mandible, that can effectively resist motion due to loading of the musculature of the tongue during swallowing and speech, and that does not damage the boney structures or nerves of the mandible.